A new retrospective case series from UCLA Stein Eye Institute reveals deeply concerning results about the toxic effects of pentosan (aka Elmiron®) to the eyes and bowel. While continued progression of retinal damage and atrophy was documented, the bowel findings were perhaps even more alarming.

In this latest study, eight patients (six women and two men) were tracked over a six-year period after exposure to pentosan polysulfate sodium (Elmiron®).(1) Participants had used the medication for a median of 25.4 years, with cumulative exposure ranging from 45.5 to 4,672 grams.  

Severe Polyposis Found In Majority of Patients

75% (6 of 8) were found to have severe colonic polyposis, the uncontrolled growth of polyps in the bowel, during routine colonoscopies.(1)  Most were asymptomatic, with no clue that their bowel had been affected. Three of the patients had a partial or total colectomy. 3/8 were also diagnosed with inflammatory bowel disease (Crohns, ulcerative colitis or microscopic colitis). 

Why the concern?  Polyposis can progress to inflammatory disease, abnormal cell growth (dysplasia), with a corresponding, increased risk of cancer, bowel obstruction, bleeding and anemia.

This is not the first paper to document changes in the bowel. Three prior studies have also documented GI changes in patients using PPS. Anderson was the first to report a significantly high rate of colonic dysplasia among IBD patients with a history of pentosan use.(2) Jung’s study found that 11 out of 13 patients who had been exposed to approximately 2000 grams of PPS developed bowel symptoms, and 9 were eventually diagnosed with IBD.  Two of these patients required colectomies.(3) Santina  found that nearly half of PPS patients (45.8%) had a history of IBD or irritable bowel syndrome… and that IBD was higher in patients with PPS maculopathy.(4)  These early papers also showed that the more PPS patients were exposed to, the greater the risk of bowel changes. 

Low Exposure Implicated

Notably, Patient #3 in the UCLA study had the lowest cumulative exposure—just 45.5 grams via subcutaneous injection for osteoarthritis—yet still developed moderate retinal damage and microscopic colitis. Another recent study identified the first reported case of pigmentary maculopathy in a patient who received pentosan polysulfate through bladder instillations, with a cumulative dosage of just 5.8 grams.(5) This is particularly important because it suggests that the risk of toxicity is not limited to patients with decades of high-dose oral use.

Progression of Retinal Atrophy Observed

Also in the UCLA study, every patient reported blurred version, and two had metamorphopsia, a symptom where lines become wavy, bent and/or distorted. A clear progression of retinal atrophy was observed over time. At the start of the study, only five eyes showed signs of retinal atrophy. By the end of the study, a total of 12 showed atrophy. 

A variety of other retinal changes were found including AVL/SHRM collapse (aka a sign of scarring), outer retinal tubulations (which occur after injury). Of particular concern was the finding of progressive choricapillaris flow deficits in 11 eyes, a reduction of blood flow that is a biomarker of retinal disease.

At first visit, 10 out of 16 eyes showed mild maculopathy, 5 were moderate and 1 was severe. At the end of the study, only 4/16 remained mild. 8 out of 16 were now moderately damaged and 4 showed severe retinal changes. 

Colonoscopies Strongly Recommended

The authors of the UCLA study recommend that all patients receiving pentosan undergo baseline and follow-up colonoscopies, even in the absence of GI symptoms. They suggested that this is a critical opportunity for urologists to work with gastroenterologists and ophthalmologists to educate patients about the “potential for life-threatening colonic disease” and the importance of early screening. 

This is also the first time a paper has suggested that the FDA re-evaluate its approval of this medication, either revoking approval or imposing tighter regulations on its use, given the “severity and irreversibility of these associated complications.” 

References: 

  1. Feo A, et al. Spectrum of Colopathy and Severe Polyposis Associated With Pentosan Polysulfate Sodium Maculopathy: A Retrospective Case Series. Am J Ophthalmol. 2026 Jul;287:1-13. –
  2. Anderson J, et al.. Pentosan polysulfate–associated dysplasia in patients with inflammatory bowel disease: a case series. Am J Gastroenterol 2023;118(5):905–908. doi:10.14309/ajg.0000000000002137.
  3. Jung EH, et al. Colopathy associated with pentosan polysulfate use. Front Pharmacol. 2025;16:1494467.
  4. Santina A, Feo A, Bousquet E, et al. Pentosan polysulfate sodium maculopathy: final analysis of a prospective cohort, updated review, and association with inflammatory bowel disease. Surv Ophthalmol. 2025;70(3):583–592.
  5. Qin S, et al. Pigmentary Maculopathy in Patients with Interstitial Cystitis: Association with Pentosan Polysulfate and Other Therapies. Ophthalmol Sci. 2025 Aug 7;6(1):100909.

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Did you know that the ICN is the only organization in the world advocating for patients struggling with retinal damage and inflammatory bowel disease associated with Elmiron® use? Our work directly helped patients receive more than $43 million dollars in compensation for retinal damage. We are now developing new data about the risk of polyposis and inflammatory bowel disease to support an expansion of the black box warning and, ideally, an FDA review of the original approval. We are the only group in the world trying to help patients who have been harmed. Would you consider donating to help us continue this vital work? We simply can’t do it without your help! MAKE A DONATION HERE!